Hi Gennaro,
As Amit suggested just check the field BEWAR is available or not in extract structure , Just hit the Tcode SE11-- > add DTFIGL_4-->display and check the field.If its available.
Follow the above suggested steps.
If field is not available need to go for cmod or badi logic.
So just find the matching fields in table BESEG and DTFIGL_4 by hitting the tcode SE11, By using this we can apply primary key and foreign key relationship between table and extract structure.
Thanks,
Somesh.